In order to regulate carbon dioxide emissions, which is the main culprit of global warming, the Kyoto Protocol took effect in December, 1997. Thereafter, in order to control huge carbon dioxide emissions, research into a renewable and clean alternative energy source that is renewable and clean such as solar energy, wind power, water power, hydrogen energy, etc., has been actively conducted.
Hydrogen has been spotlighted as clean alternative energy, which has been mainly used as an energy source of a fuel cell. The fuel cell is an energy conversion device that directly converts chemical energy included in fuel gas into electrical energy by an electrochemical reaction.
Since the fuel cell system is a direct generation system without performing a combustion process or a mechanical process, differently from an existing thermal power plant, it has high generation efficiency of 40 to 60% and has almost constant efficiency even in a wide load range of 25 to 100% of a rated output.
Further, even though the fuel cell system may reduce CO2 emissions as much as 30% or more without the combustion process, it discharges a negligible amount of NOx, SO2, and dust, which are the cause of pollution in the existing power plant and also generates very small operation noise. As a result, the fuel cell system has been in the limelight as an eco-friendly energy technology.
As applications of the present fuel cell technology, a technology has been developed for a medium-large size generation system of 100 kW to several tens MW, a home small size generation system of 1 kW to 10 kW, a car power supply, and a mobile power supply of several W to several kW has been progressed.
Among the clean energy technologies using hydrogen, a technology storing high-pressure hydrogen gas should be urgently resolved in order to use hydrogen as an energy source.
As an example, most companies other than GM have developed a fuel cell car in which a high-pressure hydrogen gas storage container is mounted. Currently, each country has competitively developed a high-pressure container withstanding 700 atmosphere since the amount of hydrogen stored in the hydrogen gas storage container determines a traveling distance.
In the high-pressure gas storage technology, it is difficult to handle hydrogen gas, which is due to strong reactivity, rapid diffusivity, light mass, etc., of hydrogen gas.
Hydrogen, which is the lightest gas, may have permeability of 80 times or more as compared with other natural gases in which it can be easily diffused and discharged to the outside of the container but may weaken a material configuring a container through chemical reaction. In addition, even though the amount of hydrogen gas discharged to the outside of the container is insignificant, hydrogen may even be combusted at a concentration even lower than a lean misfire limit. As hydrogen has a very large heating value at the time of combustion and various chain reaction paths, a development of a barrier capable of effectively preventing penetration of hydrogen is urgent for the loss and safety of the stored hydrogen.